A conventional refrigerator/freezer appliance has two compartments, one for refrigerating fresh food and the other for freezing food. The two compartments are maintained at very different temperatures, typically -20.degree. C. for the freezer compartment and +3.degree. C. for the fresh food compartment. Heat is removed from these two compartments and rejected to the ambient environment. Such refrigeration apparatus most commonly utilizes the Rankine refrigeration cycle.
The usual Rankine refrigeration circuit has a single evaporator in thermal contact with the air in the freezer compartment. Heat is removed from the fresh food compartment by circulating air between the fresh food compartment and the colder freezer compartment.
One disadvantage of this system is that all of the heat which is removed from either the fresh food compartment or the freezer compartment is removed at the considerably lower freezer temperature. Consequently even the heat from the fresh food compartment must be pumped through the higher thermal elevation from the freezer temperature to the ambient temperature. The efficiency and energy consumption of a refrigeration system can be substantially improved if the heat removed from the fresh food compartment can be removed directly from it at the fresh food temperature and elevated to the ambient temperature.
Refrigerators have also used two compressors, one for each of the two evaporators in order to achieve a higher efficiency by designing and operating each compressor at the maximum efficiency for the evaporator it supplies with refrigerant. However, this duplication of compressors increases cost and increases the volume occupied by the refrigeration equipment, consequently also reducing the refrigerated space.
Some refrigeration systems, such as that shown in U.S. Pat. No. 5,465,591, utilize a single compressor which alternatively directs the refrigerant to one evaporator or the other, but not simultaneously to both. Because the compressors used in the prior art operate at a single, constant pumping rate or displacement, such dual evaporator systems are inefficient because they have excessive capacity in the fresh food mode. Less work is required to pump heat from the higher temperature fresh food compartment because of the greater suction vapor density at the output of the fresh food evaporator.
Prior art workers have also connected evaporators in series so that one or more evaporators receive at least a portion of the refrigerant discharge from another evaporator. Such an arrangement is referred to in U.S. Pat. No. 5,228,308.
Consequently, refrigeration circuits have been constructed in the prior art in which one or multiple, conventional refrigerant compressors are connected with series or parallel connected evaporators.
Nonetheless, there remains a need to improve the efficiency of multiple compartment refrigeration systems in order to reduce the ever increasing cost of energy and improve environmental protection.